This invention relates to a preceramic polymer composed of ##STR1## units where there are present 0 to 25 mole percent [R.sub.2 Si] units and 75 to 100 mole percent [R.sub.2 SiC.tbd.CSiR.sub.2 ] units and where each R is independently selected from the group consisting of hydrogen, alkyl radicals containing 1 to 8 carbon atoms, phenyl radicals, and vinyl radicals. These preceramic polymer contain silicon atoms and carbon atoms (in the form of acetylene groups) in the polymer skeleton. Upon pyrolysis to an elevated temperature these preceramic polymers can be converted to silicon carbide-containing ceramic materials.
Preceramic polycarbosilanes (with [R'.sub.2 SiCH.sub.2 ] units), perceramic polysilanes (with [R'.sub.2 Si] and [R'Si] units), and preceramic polysilazanes are well known in the art. These preceramic polymers can be converted into ceramic materials by pyrolysis at elevated temperatures. Example of preceramic polycarbosilanes may be found in Yajima et al. U.S. Pat. Nos. 4,052,430 (Oct. 4, 1977) and 4,100,233 (July 11, 1978) where polycarbosilanes were prepared by thermally decomposing and polycondensing polysilanes. Ceramic materials were then prepared by the pyrolysis of polycarbosilanes in an inert atmosphere or in a vacuum at an elevated temperature. Examples of preceramic polysilanes may be found in Baney et al. U.S. Pat. No. 4,310,651 (issued Jan. 12, 1982) which disclosed a polysilane containing [CH.sub.3 Si] and [(CH.sub.3).sub.2 Si] units where there was present 0 to 60 mole percent [(CH.sub.3).sub.2 Si] units and 40 to 100 mole percent [CH.sub.3 Si] units and where the remaining bonds on silicon were attached to other silicon atoms and chlorine atoms or bromine atoms. The polysilanes were converted to silicon carbide-containing ceramics at elevated temperatures. Examples of preceramic polysilazanes may be found in Gaul U.S. Pat. Nos. 4,312,970 (issued Jan. 26, 1982) and 4,340,619 (issued July 20, 1982) where preceramic polysilazanes were prepared by reacting either organochlorosilanes and disilazanes or organochlorodisilanes and disilazanes. The preceramic silazane polymers could be converted to ceramic materials by pyrolysis at elevated temperatures. Numerous other examples of these types of preceramic polymers can be found in the patent and open literature.
Chandra and Zank in a copending U.S. patent application entitled "Preceramic Acetylenic Polysilanes" Ser. No. 083,121 filed Aug. 10, 1987, disclose preceramic polysilanes which contain pendant acetylenic groups attached to some of the backbone silicon atoms. The acetylenic groups were not incorporated into the polymer backbone or skeleton of the polysilane. These polysilanes could be converted to ceramic materials by pyrolysis to elevated temperatures.
British Patent No. 914,935 (published Jan. 9, 1963) discloses a method of preparing polymeric materials containing [(R".sub.2)SiC.tbd.C] units by reacting an organic difluorosilane of formula R".sub.2 SiF.sub.2 with an alkali metal acetylide. The polymers produced were used as lubricants, catalysts, and additives for plastics, varnishes, and oils.
British Patent Application No. 8,709,296 (filed Apr. 16, 1987) prepared polymeric materials containing [(R'".sub.2)SiC.tbd.C] units by reacting diethynyl silanes of formula R'".sub.2 Si(C.tbd.CH).sub.2 with an alkyl lithium salt to obtain the lithium salt of the diethynyl silane and then reacting the lithium salt with a dihalogensilane of formula R'".sub.2 SiX*2 where each R'" is independently selected from hydrogen or an alkyl or aryl group containing 1 to 18 carbon atoms and where X* is a halogen atom. Suggested uses include semiconductor, photoconductor, and optical waveguide applications.
More recently, Seyferth, at the Eighth International Symposium on Organosilicon Chemistry held at St. Louis, Mo. on June 7-12, 1987, disclosed preceramic polymers containing [(CH.sub.3)R.sup.iv SiC.tbd.C] units where R.sup.iv is hydrogen, methyl, or vinyl. These preceramic polymers were prepared by reacting acetylene Grignard with an organosilane of formula (CH.sub.3)R.sup.iv SiCl.sub.2. The preceramic polymers could be converted to ceramic materials in about 60 to 85 weight percent by pyrolysis to elevated temperatures.
The preceramic polymers of the present invention containing ##STR2## units, where there are present 0 to 25 mole percent [R.sub.2 Si] units and 75 to 100 mole percent [R.sub.2 SiC.tbd.CSiR.sub.2 ] units and where each R is independently selected from the group consisting of hydrogen, alkyl radicals containing 1 to 8 carbon atoms, phenyl radicals, and vinyl radicals, appear to be novel compositions of matter. Such preceramic polymers are useful in preparing ceramic materials by pyrolysis at elevated temperatures.